Shielded ultra high frequency tuning apparatus



F. c. ISELY 2,557,969

SHIELDED ULTRA HIGH FREQUENCY TUNING APPARATUS June 26, 1951 2 Sheets-Sheet 1 Filed Dec. 29, 1948 INVENTOR. FRANK C. ISELY ATTORNEY June 26, 1951 F. c. ISELY 2,557,969

SHIELDED ULTRA HIGH FREQUENCY TUNING APPARATUS Filed Dec. 29, 1948 2 Sheets-Sheet 2 INVENTOR. FRAN K C. ISELY Patented June 26, 1951 SHIELDED ULTRA HIGH FREQUENCY TUNING APPARATUS Frank C. Isely, Washington, D. 0.

Application December 29, 1948, Serial No. 67,905

(Granted under the act of March 3, 1883, as

'7 Claims.

amended April 30, 1928; 370 G. 757) The present invention relates to ultra-high frequency tuning apparatus, and is particularly concerned with the problem of providing a tun able line controlled (distributed constant) circuit wherein tuning may be accomplished without varying the physical length of the line.

'. Another object of the present invention is to provide ultra high frequency apparatus readily tunable over a wide frequency range.

Another object of the present invention is to provide a simple, inexpensive distributed constant tuning circuit.

Still other objects and features of the present invention will become apparent upon carefulconsideration of the following detailed description when taken together with the accompanying drawings, in which:

Figs. 1 and 1A are partial sectional front and side views respectively of one embodiment of the invention.

Figs. 2 and 2A are partial sectional front and side views of a second embodiment of the present invention.

Referring now more particularly to Figs. 1 and 1A there is shown in detail an anti-resonant shielded line tuner constructed in accordance with the teachings of the present invention. This embodiment is in the nature of a quarter wave concentric line section and comprises a tubular inner conductor I0 shielded by a box like outer conductor II. The latter consists of front and back end plates I3 and I2 and four side plates which are undesignated. V The inner conductor II), as hereinafter described, is shorted at radio frequencies to end plate I3 of outer conductor II and is rotatably supported in coaxial relation with respect to said end plate by a stationary center post I 4.

Center post I4 serves both as a bearing support and as a short circuiting capacitor for the tubular inner conductor I0. As a bearing support, center post I4 is bolted to the end plate I3 by screw I6, which for reasons soon to become apparent is insulated from end plate I3 by fiber washer I1. A pair of flanged brass sleeve bearings I9 and are inserted in opposite ends of the inner conductor and snugly surround the center post I 4 to provide suitable bearing surfaces for the inner conductor and to provide a conductive path between the same and the center post l4.

As a short circuiting capacitor, center post I4 terminates in a fiat circular flange plate I5 which fits into a circular recess I5A formed in the end plate I3. A sheet of mica I8 insertedin the recess I5A between the flange plate I5 and the end plate I3 insulates the center post from the end plate. Flange plate I5 and end plate I3 are thus seen to form the two plates of a short circuiting capacitor, while the mica I8 serves as the dielectric therefor.

To provide rotation of the inner conductor III, the same is terminated at the end thereof adjacent end plate I3 in an integrally formed gear wheel 2I. Engaging gear wheel 2| is a suitable fiber spur gear 22 mounted in a circular recess 22A milled on the inside face of the end plate I3 adjacent the first recess I5A. Fiber spur gear 22 is keyed to a shaft 23. The latter emerges from end plate I3 and terminates in a suitable tuning knob 24.

To tune the line a set of stator plates 26 uniformly spaced along substantially the full length of the line is mounted on the inside of the side walls of the outer conductor II and extend inwardly in toward the inner conductor I0. Mounted on the inner conductor I 0 and rotatable therewith is a set of rotor plates 25 uniformly spaced along substantially the full length of the inner conductor I ll. Rotor plates 25 are arranged to mesh with the stator plates 24 whereby the distributed capacitance of the line and hence the tuning of the line may be varied with rotation of the inner conductor I0.

In operation, the maximum frequency to which the circuit may be tuned is attained when the rotor plates are fully out of mesh with the stator plates. In this condition the resultant frequency of the circuit is governed by the electrical length of the center conductor I 0 plus whatever lengthening effect the fringe capacity between the rotor and the stator condenser plates has on the circuit. In practice the center conductor I0, is of course, cut to approximate an electrical quarter wavelength at the highest frequency to which the circuit is to be tuned.

The minimum frequency to which the circuit tunes obtains when the rotor plates 25 are full meshed with the stator plates 26.

From the foregoing it becomes apparent that in using the present invention as an R. F. tank circuit, such as a wave trap, suitable energy input and output electromagnetic or electrostatic energy probes, not shown, may be inserted into the circuit at any suitable point. It is also apparent that while the present embodiment has been described as being so dimensioned as to function in a one quarter wave resonant mode, other odd electrical quarter wave modes also may 3 be employed without departing from the spirit of the invention.

In the present embodiment of the invention the stator plates are shown as being trapezoidal and the rotor plates semi-circular. This representation is, of course, solelyfor the purpose of illustration and is not a limitation in that'the respective shapes of the condenser plates may assume any suitable configuration.

In some instances it might be desired to so form the plates as to produce a'straight :line frequency variation, whereas in other instances a logarithmic frequency variation may bedesired.

In employing the present embodiment in the production of oscillations a light house.

vacuum tube 30 may be introduced into .the circuit as illustrated in Fig. 1A.

To this end, end plate 12 of the outer conductor is apertured at 3| just above the center conductor Ill. The aperture 3| is lined with a flexible annular contact ring 32 adapted toengage the grid ring terminal of the light house tube' 30, while the center post I4 is slotted as shown at 34 to permit contact with the plate cap of the tube 30.

Appropriate 13* potential may'be'connected'to screw IE to provide suitable'plate supply potential for the tube. 'Thecathode ring terminal 35'of tube30 is seated in a flexible annular contact ring 35 supported by an annular member 31. The latter in turn is insulated from and mechanically fixed to end plate l2 by a plurality of stand-off insulators 38.

To provide regenerative feedback, the cathode is el ctrostatically coupled to the anode circuit bya suitable capacitive feedback strap 39. Strap 39 is fed through an aperture to cut in the end cover |2, and is conductively attached at one end to the cathode contact or support 31 and'terminated at its other end in capacitive relation to the anode.

In the embodiment shown in Figs. 1 and 1A it'will be recognized that a sliding contact exists between the center post I l and the inner conductor H). In certain applications, such sliding contact maygive rise to undesirable noise and the embodiment illustrated in Figs. 2 and 2A maybe preferred.

In the embodiment of Figs. 2 and 2A, to which referenceis'now made, the inner conductor of the line is made stationary and a split stator type of tuning arrangement'is employed, whereby sliding contacts are avoided.

In particular the inner conductor I is set-off from the axis of the outer conductor II and is again provided with an R. short to the end plate I3 by means not shown. The inner conductor ||l contains a niche 4| into which a slotted contactor 40 may be inserted to engage the plate can of a light house tube much as in the'same manner as hereinbefore described. A sheet of mica 42 is placed in the niche 4| to insulate the contactor from the inner conductor H3, while a screw I6 is again used'to hold the contactor 40 in place and to provide a terminal for supplying a plate supply connection to the contactor 40.

For tuning purposes, two sets of stator plates areemployed. One set M is uniformly distributed along the length of the inner conductor H! and extends laterally away therefrom. The other set 45 is attached to one of the side walls of the outer conductor and extends laterally away therefrom in matching relation to the .platesof thefir'st set. interposed between the -:meshing with at least one set of stators.

For the purpose of raising the high frequency end to its uppermost limit, the rotor plates are so shaped relative to the stator plates that when the rotor .plates are positioned to fully mesh with one set of stator plates, namely 45, no meshing with the other set 44 exists.

To prevent the occurrence of spurious modes of operation, the rotor plates are mounted on an insulating shaft 41, whereby each rotor plate is insulated from the other.

In other respects the arrangement of this embodiment is substantially identical tothat shown in'Figs. 1 and 1A, both; in its constructionv and inapplication. Here again, however, and' for purposes. of simplification, no energy input or output probes or loops are shown.

Although I have shown and described 'only certain and specific embodiments of thepresent invention it will be readily understood. that numerous other modifications and embodiments are possible thereof without departingfrom' the spirit of the invention.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without'the payment of any royalties thereon or therefor.

What is claimed is:

l. A tunable ultra-high frequency circuitcomprising, a pair of essentiallyco-extensive, parallel conductors equal in length to an odd number of electrical quarter wave-lengths at 'the highest frequency of operation, a set of condenser stator plates attached to and uniformly distributed over substantially thefull'leng'th of at least one of said conductors and extending laterally away therefrom toward the other conductor, a set of condenser rotor plates rotatably positioned to mesh with said stator plates and operative to uniformly vary the distributed capacity between the conductors, and-a high frequency short circuit connecting means separate from said condenser plates connected across one pair of adjacent ends of said conductors.

2. A tunable ultra-high frequency circuit comprising, a pair of parallel conductors equal in length to an electrical quarter wave-length or multiple thereof at the highest frequency of op eration, a separate set of condenser stator plates attached to and uniformly distributed over substantially the full length of each of said conductors, each of said setsof stator plates extending laterally away from its respective conductor toward the other conductor, a setof condenser rotor plates rotatably positioned to meshwith said stator plates and operative to uniformly vary the distributed capacity between the conductors.

3. A tunable ultra-high frequency circuit comprising, a pair of essentiall co -extensive parallel conductors equal in length to an odd number of electrical quarter wavelengths at the highest frequency of operation, means providing a high frequency short circuit between 'cne pair of adjacent ends of' said conductors, a separate s'et'of condenser stator plates attached to and uniformly distributed "over substantiallythefull length of each of said conductors, each of said sets of stator plates extending laterally away from its respective conductor toward the other conductor, a set of condenser rotor plates rotatably positioned to mesh with said stator plates and operative to uniformly vary the distributed capacity between the conductors.

4. A tunable ultra-high frequency circuit comprising, a pair of conductors equal in length to an electrical quarter wave-length or multiple thereof at the highest frequency of operation, one of said conductors being larger in diameter than the other, the conductor of larger diameter surrounding the other so as to form a line section having inner and outer conductors, a set of condenser stator plates attached to and uniformly distributed over substantially the full length of at least one of said conductors and extending laterally away therefrom toward the other conductor, a set of condenser rotor plates positioned to mesh with said stator plates and operative to uniformly vary the distributed capacity between the conductors.

5. A tunable ultra-high frequenc circuit comprising, a pair of conductors equal in length to an odd number of electrical quarter wavelengths at the highest frequency of operation, one of said conductors being larger in diameter than the other, said one of said conductors surrounding the other so as to form a shielded line section, means providing a high frequency short circuit between one pair of adjacent ends of said conductors, a set of condenser stator plates attached to and uniformly distributed over substantially the full length of at least one of said conductors and laterally extending away therefrom toward the other conductor, a set of condenser rotor plates positioned to mesh with said stator plates and operative to uniformly vary the distributed capacity between the conductors.

6. A tunable ultra-high frequency circuit comprising, a pair of conductors equal in length to an odd number of electrical quarter wavelengths at the highest frequency of operation, one of said conductors being larger in diameter than the other, said one of said conductors surrounding the other so as to form a shielded line section, means providing a high frequency short circuit between one pair of adjacent ends of said conductors, a separate set of condenser stator plates attached to and uniformly distributed over substantially the full length of each of said conductors, each of said sets of stator plates extending laterally away from its respective conductor toward the other conductor, a set of condenser rotor plates rotatably positioned to mesh with said stator plates and operative to uniformly vary the distributed capacity between the conductors.

7. A tunable ultra-high frequenc circuit comprising, a pair of conductors equal in length to an odd number of electrical quarter wavelengths at the highest frequency of operation, one of said conductors being larger in diameter than the other, said one of said conductors surrounding the other so as to form a shielded line section, means providing a high frequency short circuit between one pair of adjacent ends of said conductors, a, separate set of condenser stator plates attached to and uniformly distributed over substantially the full length of each of said conductors, each of said sets of stator plates extending laterally away from its respective conductor toward the other conductor, an insulated rotor shaft, a set of condenser rotor plates mounted on said shaft and rotatably positioned to mesh with said stator plates, thereby to uniformly vary the distributed capacity between the conductors.

FRANK C. ISELY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,938,334 Hoffman Dec. 5, 1933 2,183,123 Mason Dec. 12, 1939 2,193,500 Usselman Mar. 12, 1940 2,359,618 Byrne Oct. 3, 1944 2,384,594 Thias Sept. 11, 1945 2,413,836 Larson Jan. 7, 1947 OTHER REFERENCES A New Approach to Tunable Resonant Circuits for the 300 to 3000 Inc. Frequency Range, Proceedings of the I. R. E., vol. 36, No. 8, August 1948, using page 1018. 

